Wheat and barley are the most important cultivated grain crops in the world as well as one of the main food crops in China. Grain crops are often confronted with the threat of fungal diseases such as smut, head blight, powdery mildew, rust, leaf blight, sheath blight and eye pot. These diseases may occur in worldwide grain growing regions, severely affecting the yield and quality of agricultural grain products. Especially, Fusarium head blight caused by Fusaria not only can result in devastating yield loss, but also can produce toxins, such as deoxynivalenol (DON) and zearalenon in infected grains, consequently, the quality of food, such as fermented food and brewed liquors, is severely affected, and the health of the human being and animals are harmed.
The deoxynivalenol toxin includes DON, 3A DON and 15A DON toxins, which have acute and chronic toxicity to human being and animals. As the DON toxin has stable chemical properties and won't be decomposed when heated, the DON toxin widely exists in head blight fungus-infected barley and wheat, processed food thereof and animal products fed with grains infected by head blight fungi. It has been known that the main symptoms of human and animal poisoning caused by the DON toxin include nausea, emesis, dizziness, drowsiness, headache, numb hands and feet, general weakness and decrease in immunity, the fluctuation of breath, pulse, body temperature and blood pressure, bleeding, miscarriage and even death can be seen in severe cases, and the DON toxin can cause human Kaschin-Beck disease (KBD) and has obvious embryotoxicity and teratogenic and carcinogenic effects. Since the DON toxin has severe harm to human health. In the joint conference on food additives and contaminants held in Geneva in October, 1973, the United Nations world food and agriculture organization (FAO) and the world health organization (WHO) decided to include Fusarium toxins into the fifth topic among sixteen topics given priority in research, and many countries have also always considered the control of head blight as an important research topic.
Moreover, many international organizations and national health organizations have laid down corresponding laws and regulations to strictly limit DON toxin content in food. FAO provides that the content of DON in food must be less than 1 mg/kg, and WHO provides that the content of the DON toxin in food and feed cannot respectively exceed the standards of 1 mg/kg and 5 mg/kg. The European Union food safety standard requires that the content of the DON toxin cannot exceed 0.75 mg/kg in edible kernels and cannot exceed 0.5 mg/kg in bread and other foods. The national standard established by the Ministry of Health in China provides that the content of the DON toxin in edible wheat flour and corn cannot exceed 1 mg/kg.
Fusarium head blight is an ascomycete disease, including bud rot, seedling blight and ear rot/ear blight, caused by a variety of Fusaria (Fusarium spp.). It includes nearly twenty varieties of pathogens, such as Fusarium graminearum (F. graminearum), Fusarium asiaticum (F. asiaticum), Fusarium culmorum (F. culmorum), Fusarium avenaceum (F. avenaceum), Fusarium moniliforme (F. moniliforme) and Fusarium nivale (F. nivale). Fusarium head blight in most of the regions in China is caused by the mixed population of Fusarium graminearum (F. graminearum) and Fusarium asiaticum (F. asiaticum), F. asiaticum is mainly in the southern wheat region, and F. graminearum is mainly in the northern wheat region.
As no grain crop varieties or gene resources which are immune or highly resistant to Fusaria have been found as yet, using fungicides has become the only effective Fusarium head blight control technology. For almost a century, people have been carrying out a great deal of work to research and develop fungicides for grain fungal diseases, and have developed inorganic fungicides, organosulfureous fungicides and aromatic hydrocarbon protective fungicides in succession, especially selective fungicides developed after 1960s, such as benzimidazole fungicides, ergosterol biosynthesis inhibitors, cytochrome b inhibitors and succinodehydrogenase inhibitors, so that the epidemic harm of a lot of important grain crop diseases, such as grain crop smut, powdery mildew, rust, leaf blight and eyespot, has been effectively controlled. However, as the deoxynivalenol (DON) toxin produced by Fusarium (Fusarium spp.) has the function of a pathogenic factor, the resistance to a variety of fungicides is enhanced, and as a result, the control effect of the majority of fungicides on Fusarium head blight is not very ideal. Therefore, how to effectively control grain crop head blight is a current significant social demand in guaranteeing grain safety and food safety.
The DON toxin contamination level of diseased grain depends on the quantity of pathogenic fungi infecting the grain and the toxin biosynthesis capability of thalli. Aimed at the situation that the control effect of today's domestic and foreign main fungicides for controlling Fusarium head blight is not ideal and that DON toxin contamination often exceeds edible safety standards, the present invention studies and discovers two types of β1-tubulin (β- and β2-) receptors for benzimidazole fungicides existing in Fusaria and a genetic negative regulation mechanism for fungicide resistance and fungicide sensitivity for the first time, and discovers that the 240th amino acid phenylalanine composing the β2-tubulin receptor is a main cause of fungicide sensitivity decrease and that the point mutation of the 167th amino acid will cause carbendazim to lose the control effect and greatly enhance the DON toxin synthesis capability, mycelial colonization speed and pathogenecity of thalli, decreasing the control effect of fungicides; in addition, the study also discovers an ergosterol biosynthesis inhibitor (EBI) receptor of Fusarium, i.e. cytochrome, P450 monooxygenase (Cyt.p450), or fungicide sensitivity or fungicide resistance to EBI can be decreased by the overexpression or point mutation of encoding genes. Therefore, although some fungicides show very high activity in the lab, high dosages are needed when the fungicides are applied in fields, for example, 40 g to 50 g (600-750 g a.i./hm2) of benzimidazole fungicide with above active ingredients or 15 g to 20 g (225-300 g a.i./hm2) of EBI with above active ingredients need to be used per mu to obtain about 70 percent of Fusarium head blight control effect.
As these selective fungicides with single acting mechanisms are used in a large amount for a long term, fungicide resistance will appear in pathogenic fungus populations in the nature, and the effect in use will decrease year by year. After nearly thirty years of fungicide resistance monitoring, the inventor discovers that Fusaria which have developed fungicide resistance to benzimidazole fungicides, such as carbendazim, have formed a dominant population in Eastern China, and the commonly used benzimidazole fungicides, such as carbendazim and thiophanate-methyl, have almost lost the value in controlling Fusarium head blight. Furthermore, because the capability of fungicide-resistant pathogenic fungi in producing DON toxin is not less than five times the capability of sensitive strains, the harm of Fusarium head blight and the risk of food safety in China are increasingly exacerbated. In order to reduce yield loss, farmers often double the use of fungicides, such as carbendazim, and as a result, fungicide resistance, pesticide residue, environment pollution and food safety problem are further exacerbated.
Therefore, the inventor finally accomplishes the present invention through a great deal of experimental research and analysis on the basis of summarizing the prior art.